Such a continuously variable toroidal drive usually has input and output disks disposed co-axially in relation to a common shaft and arranged in pairs to define toroidal inner surfaces with friction wheels disposed between the pairs of input and output disks. The fiction wheels are in frictional contact both with the input disks and with the output disks and transmit the torque transmitted by them from the input disk to the output disk by frictional engagement, the speed of the friction wheels being higher the greater distance between their contact point with the input disk and the axis of the disks rotation. The speed of the output disks, on the other hand, is higher the closer the contract between friction wheel and output disk is to that axis of rotation. Accordingly, by swiveling the friction wheels, the speed of the output disk can be continuously adjusted as desired. To this end the axes of rotation of the friction wheels are supported on a carrier which is controllable by a swiveling device.
The fundamental principle of such a continuously variable toroidal drive has already been described in U.S. Pat. No. 2,152,796 which was published in the year 1939. Therein are provided two pairs of concave input and output disks between which are situated tiltably supported friction wheels so that a torque transmitted, via an input shaft, to the input disks and the friction wheels, depending on the relative position of the friction wheels with a reduction ratio independent thereof, via the output disks, a gear stage and a hollow shaft to a summation gear unit in the form of planetary gear. The web of the planetary gear drives an output shaft which is connected, for example, with the input gears of a motor vehicle. The output shaft can be disposed parallel to the output shaft and spaced therefrom. The output gear and the two output disks are rotatably supported on the sleeve which at its ends is supported in bearing brackets. The arrangement of the bearing brackets respectively between an input and output disk presupposes a sufficiently large space between said disks.
The gear unit according to the U.S. Pat. No. 3,739,658 also has a pull-and-push variator with two input and output disks disposed in pairs between which are situated tiltably supported friction wheels. In said construction, there is a bearing bracket that is a component part of the housing and is spatially situated between the two output disks. The power flowing from the output disks is fed via a planetary gear, which in addition acts as differential, to a hollow shaft. The hollow shaft is non-rotatably connected with the output gear and rotatably held by ball bearings in the bearing bracket.
The output gear is in operative connection with a gear which is secured non-rotatably to the housing of a torque converter. The latter drives the output shaft of the gear unit. The arrangement of the torque converter on the input of the output shaft implies a relatively large center distance between input and output shafts of the gear unit. The use of said gear unit are narrowly limited, since the installation space required is not always available.
From U.S. Pat. No. 5,067,360 has become known a continuously variable toroidal drive having an input shaft that penetrates a housing front wall and two pairs of toroidal input and output disks between which are situated also tiltably supported friction wheels by means of which the desired reduction ratio can be set. With the input shaft is associated a cam flange firmly connected with it which acts upon a roller-shaped pressure device in direction of the first input disk which is firmly connected with a torque shaft which penetrates the gear unit. The second input disk is also firmly connected with the torque shaft and thereby is offset in rotation while the two output disks arranged mirror symmetrically to each other and between the two input disks are rotatably supported on the torque shaft and jointly act upon an output gear in direction of an output shaft.
German Patent Application No. 197 03 544 describes a gear unit in which the input power is directly transmitted in a first power range from an input shaft to an output shaft and in a second power range is transmitted via a continuously variably adjustable toroidal drive having interacting toroidal treads disposed in pairs between which roller bodies move and a planetary gear wherein the first power range corresponds to a first forward drive range in which the input power is transmitted via the variator to the output shaft, while the planetary gear rotates as unit and wherein on the first power range another power range adjoins which corresponds to a range of higher forward drive speed in which the input power is fed with power distribution directly and via the variator to the planetary gear and through this is transmitted cumulatedly to the output shaft.
In toroidal drive systems with power distribution there often appears during shifting, high amplitudes of the torque which, when using the customary mechanical axially acting pressing devices, lead to turning angles between the two spaced apart input disks. Besides, in toroidal drive systems with power distribution, variator torque in the power distributed range is unequal to the engine torque. Since the pressing device is torque dependent, both input disks must draw together and this takes place via angular disks in which the forward input disk on the input side, is rotated by up to 60.degree. relative to the shaft and thus relative to the rear input disk. In a push/pull change the complete turning angles are achieved in well under a second.
For the pressing devices, designed as rollers, this means accelerations or decelerations on the forward input disk which the rollers on the rear do not experience. Depending on the acceleration or deceleration, this increases the slip on the forward and rear rollers.
The problem on which the present invention is based is to prevent any angular twists between the front and rear input disks in a power distribution toroidal drive where the axial force is transmitted via a roller-shaped pressure device.